The present invention relates to an apparatus for preventing the unraveling (also hereafter referred to as xe2x80x9cravelingxe2x80x9d) of a seam at the end of sewing, the apparatus being provided in a sewing machine such as a double chain stitch sewing machine or a covering chain stitch sewing machine for sewing cloth with a looper thread and needle threads.
In a double-ring-sewing sewing machine or a flat-sewing sewing machine for sewing cloth by using needle threads and a looper thread, a loop of needle threads 6a and 6b and a looper thread 7 are intertwined in a form of another thread loop on a rear surface of a sewing cloth, so that a seam shown in FIG. 1A is formed. Such seam has a problem in that the looper thread 7 is pulled out from the final loops 6c and 6d by pulling the looper thread 7 cut at the end of the sewn portion, so that such pulling out progresses toward the start of sewing and the seam formed as shown in the drawing is raveled from the end of sewing.
In order to prevent such raveling of the seam, conventionally two methods have been generally used: a first method allows sewing in several stitches before the end by shortening the distance between seams on the sewing cloth or reducing the tension of the needle thread, so that the needle threads and the looper thread intertwine more easily between stitches near the end of sewing. A second method allows the needle thread to be tightened by increasing the tension of the looper thread next to the sewing cloth immediately before the end of the sewing.
However, there is a problem in the first method in that the seam in the vicinity of the end of sewing has a form different from the other portion thereof, or the seams look slack as a whole, so that the external appearance of the sewn product becomes poor and besides the needle threads and the looper thread are not necessarily intertwined as desired, so that a secure effect of preventing the raveling of the thread cannot be obtained. There is also a problem in the second method as well in that a wrinkle is generated on a sewn cloth in the vicinity of the end of sewing along with the tensioning of the needle thread, so that the external appearance becomes poor and a sufficient effect of preventing the raveling of the thread cannot be obtained.
Under these circumstances, the inventors of the present invention propose in Japanese Patent Publication No. 2879399 a method and an apparatus for preventing the raveling which provide a secured effect in preventing the raveling without the deterioration in the external appearance. The method and the apparatus are such that a looper thread hanger (a looper thread hanging hook) is provided for holding the looper thread, which is allowed to pass through the loop of the needle thread with the advance of the looper, on the side of the advancing end of the looper, the sewing operation is temporarily suspended with the looper being in the state of advancing, followed by catching the looper thread on the looper thread hanging hook so that one stitch is sewn in this state and the needle thread and the looper thread are cut.
According to this method, as shown in FIG. 1B, the looper thread 7 caught on the looper thread hanging hook remains in the form of another thread lacing on the final loops 6c and 6d of the needle thread 6a, 6b formed before the suspension of the sewing operation, and the looper thread 7 is not pulled out from the final loops 6c and 6d even when the end portion is pulled, with the result that the raveling of the seam can be prevented with certitude. Furthermore, as shown in the drawings the seam on the end portion of the sewing does to seem to be different from the other portion and the external appearance is not deteriorated.
In this manner, the method and the apparatus for preventing the raveling which are proposed in the Japanese Patent Publication No. 2879399 are excellent method and apparatus which can prevent the raveling of the thread generated on the seam at the end of the sewing in a sewing machine for sewing cloth by using a looper thread and needle threads such as the double-ring-sewing sewing machine, flat-sewing sewing machine or the like. The same method and apparatus are also disclosed in Japanese Patent Application Laid-Open No. HEI-910-225163, Japanese Patent Application Laid-Open No. HEI-11-57253, Japanese Patent Application Laid-Open No. HEI-11-57268 and Japanese Patent Application Laid-Open No. HEI-11-70281.
The apparatus conducting a method for preventing raveling of the seem as described above is constituted in such a manner that a looper thread hanging hook for catching the looper thread is arranged on the side of the advance end of the looper which advances from the right side of the needle drop point to the left side thereof, namely the rear side of the left of the needle drop point, so that an advance or retreat operation at the point or a swing operation around a vertical axis is conducted to catch the looper thread on the rear side of the looper.
However, for the arrangement of the looper thread hanging hook including a driving mechanism for the advance or retreat operation or a swing operation of the looper thread hanging hook, a large space is required on the left side of the needle drop point, namely, at the tip side of the sewing bed of the sewing machine. In particular, in a sewing machine provided with a small diameter cylinder-shaped bed for handling a cylindrically sewn product, the tip portion of the bed is extended for securing an arrangement space of the looper thread hanging hook, so that it is feared that the sewing operation is prevented.
The present invention has been made in view of the above circumstances, and an object of the invention is to provide an apparatus for preventing the raveling of a seam, the apparatus realizing a method for preventing the raveling disclosed in the Japanese Patent Publication No. 2879399 without requiring a large arrangement space on the tip side of the sewing bed of a sewing machine by arranging a looper thread hanging hook and a driving mechanism thereof together with a cutting mechanism of the looper thread and the needle thread, on the right side of the needle drop point, the apparatus being applicable to a sewing machine provided with a cylindrical bed in which the arrangement space on the tip side is restricted.
According a first aspect of the present invention, there is provided an apparatus for preventing raveling of a seam, which is provided on a sewing machine for sewing a product by allowing a looper which advances from the right side to the left side of a needle drop point to pass through a loop of a needle thread formed at the needle drop point to force the looper thread held by the looper to twine around the needle thread, said apparatus comprising:
a loop thread hanging hook arranged on the right rear side of the needle drop point to advance or retreat and catches the looper thread in the vicinity of the advance end of the looper at the time of the advance thereof;
a needle thread cutting hook arranged on the right side of the needle drop point to advance ro retreat and catches the needle thread being inserted into the loop of the needle thread at the time of the advance thereof;
a needle thread knife slidably contacting the needle thread cutting hook at the time of the retreat of the hook, the knife cutting the needle thread which is caught at the time of the advance of the needle thread cutting hook;
a looper thread cutting hook arranged on the right side of the needle drop point to advance or retreat and catches the looper thread caught by the looper thread hanging hook at the time of the advance thereof;
a looper thread knife slidably contacting the looper thread cutting hook at the time of the retreat of the hook, the knife cutting the looper thread caught at the time of the advance of the loop thread cutting hook; and
a looper thread cutting hook arranged on the right side of the needle drop point to advance or retreat and catches the looper thread caught by the looper thread hanging hook at the time of the advance thereof;
a looper thread knife slidably contacting the looper thread cutting hook at the time of th retreat of the hook, the knife cutting the looper thread caught at the time of the advance of the loop threat cutting hook; and
means for controlling an operation of preventing the raveling of the seam, the mans causing the sewing machine to temporarily suspend the sewing operation before the end of the sewing in the state in which the looper advances followed by forcing the looper thread hanging hook to advance to catch the looper thread and then forcing the hook to retreat, then forcing the sewing machine to conduct the sewing operation for on stitch in this state, which is then followed by forcing the needle thread cutting hook and the looper thread cutting hook to advance and retreat thereby cutting the needle thread and the looper thread with the needle thread knife the looper thread knife respectively.
In the first aspect of the present invention, the looper thread hanging hook arranged at the rear side of the right of the needle drop point is forced to advance and is operated to catch the looper thread at the rear side of the looper which exists at the advance end, so that the sewing machine is forced to conduct one stitch sewing operation followed by forcing the needle thread cutting hook and the looper thread cutting hook arranged on the right rear side of the needle drop point to advance thereby the needle thread cutting hook being inserted into the loop of the needle thread. This allows the looper to pass therethrough to catch the needle thread, and the looper thread cutting hook catching the looper thread held on the looper thread hanging hook so that the needle thread knife and the looper thread knife are forced to slidably contact the hooks to cut the threads respectively at the time of the retreat of the both hooks thereby preventing the raveling.
In the first aspect of the present invention, the looper thread hanging hook for temporarily holding the looper thread immediately before the end of sewing is arranged on the right side of the needle drop point together with the needle thread cutting hook and the looper thread cutting hook in order to prevent the raveling. Since these hooks and the driving mechanism are arranged on the right side of the needle drop point, the prevention of the raveling can be realized without the need of a large space at the tip side of the sewing bed. Thus, the first aspect of the invention can be applied irrespective of the kind of sewing machines, such as a sewing machine provided with a cylindrical bed in which the arrangement space on the tip side thereof is restricted. As a result raveling of the seam can be prevented in a simple operation, no wrinkle is generated on the sewn cloth, and there is no deterioration of the external appearance, even with an unusual state of the seam.
Furthermore, according to a second aspect of the invention, the apparatus for preventing the raveling of the seam according to claim 1, further comprises a looper thread holding hook continuously provided at the tip portion of the needle thread cutting hook for catching the looper thread in the vicinity of the advance end of the looper at the time of the advance of the needle thread cutting hook, pulling out the caught looper thread from the final loop of the needle thread at the time of the retreat of the needle thread cutting hook after the advance, to hold the looper tread in front of the needle knife.
In the second aspect of the invention, when the needle thread cutting hook advances to be inserted into the loop and catches the needle thread, the looper thread holding hook which is continuously provided at the end of this needle thread cutting hook catches and holds the looper thread in the vicinity of the end of the looper, namely, at the side of the looper rather than at the cutting position by the looper thread cutting hook, with the result that the disposition of the looper thread becomes unnecessary at the time of the start of the next sewing operation.
Furthermore, according to a third aspect of the invention, the apparatus for preventing the raveling of the seam according to claim 2, further comprises thread pulling back means for pulling back the looper thread before the supply to the looper in order to shorten the hanging length of the looper thread caught by the looper thread holding hook.
In the third aspect of the invention, the looper thread ahead of the supply to the looper is pulled back, the length of the looper thread held on the looper thread holding hook is shortened, and the accompanying of the long looper thread on the sewing start portion at the time of the next sewing operation is prevented, with the result that disposal of the looper thread is unnecessary.
Furthermore, according to a fourth aspect of the invention, the apparatus for preventing the raveling of the seam according to claim 3, further comprises:
a looper thread guide for holding the looper thread before the supply to the looper so as to cross the advance and retreat path of the needle thread cutting hook; and
a thread hooking portion provided on the needle cutting hook or on a part of an attachment base thereof to hook the looper thread held along the looper thread guide at the time of the retreat of the needle thread cutting hook.
In the fourth aspect of the present invention, a thread hanging portion is provided on the needle thread cutting hook integrally with the looper thread holding hook or on a part of the holder of this needle thread cutting hook, and by utlizing the ratreat motion of the needle thread cutting hook for cutting the needle thread, the looper thread held along the looper thread guide so as to cross the retreat path during this motion is caught by the needle hooking portion and is pulled back thereby shortening the length of the looper thread held on the looper thread hook.
In the fourth aspect of the invention, the length of the looper thread held on the looper thread holding hook can be shortened without using a special apparatus thereby making it possible to prevent the deterioration in the external appearance with a simple structure.
The above and further objects and features of the invention will more fully apparent from the following detailed description with accompanying drawings.